1. Field of the Invention
The present invention relates to elevator systems. In particular, the invention relates to a method and system for allocating destination calls in an elevator system comprising both single-deck and multi-deck elevators.
2. Background of the Invention
Tall buildings typically contain numerous elevators, escalators and other corresponding conveying means for transporting people from one floor to another in the building. When a passenger inputs a call for an elevator, the group control function of the elevator system allocates an elevator to serve the passenger according to the situation prevailing in the elevator system and on the basis of given optimization criteria. In a conventional elevator system, call entry is arranged by providing each floor of the building with up/down buttons, by means of which the passenger indicates the desired traveling direction and, further, after the elevator has arrived at the floor where the passenger is located, the passenger indicates the desired destination floor by means of floor selection buttons provided in the elevator car. However, the above-described call entry method is impractical and inefficient in tall buildings, which is why call entry in the elevator systems in such buildings is increasingly implemented using a so-called destination call system, wherein each passenger gives his/her individual destination data already at the starting floor, e.g. in the elevator lobby before boarding an elevator car. A destination call is input via a specific destination call terminal using either buttons and/or electrically readable identifiers, such as e.g. RFID identifiers. As the starting and final points of the route to be traveled by each passenger are identified in connection with the destination call and are therefore available to the group control, the group control system is able to determine the passenger's route accurately and optimally as compared to the traditional call entry system.
Allocation of calls entered by passengers aims at estimating different route alternatives for the passengers and assigning the calls to be served by the elevators so as to optimize one of the indicators describing the elevator system or a combination of such indicators. Traditionally, the most commonly used indicators relate to passenger service times, but it is also possible to use optimization criteria relating to energy or some other corresponding property of the elevator system. To compare different route alternatives, a so-called cost function is generally used, minimization of whose value (total cost) for different route alternatives indicates optimal allocation. Allocation can also be so implemented that in different traffic situations the cost function best suited for the particular situation is applied. The purpose of this is to allow the system to adapt to the prevailing traffic situation, e.g. an up-peak traffic situation in the building. A relevant description of the technique in question is found e.g. in patent specification FI972937, which discloses an elevator group control method whereby the control of the elevators is optimized on the basis of the traffic situation, i.e. the prevailing traffic type and traffic intensity, by identifying the prevailing traffic situation and controlling the elevator group on the basis of optimization criteria corresponding to the aforesaid traffic situation. To identify the prevailing traffic situation, statistical data is collected on the operation of the elevator system according to different times of the day and different days of the week, and a forecast on the future state of the elevator system at each instant of time is produced on the basis of the statistical data collected. The solution in question is termed ‘traffic forecaster’.
To improve the efficiency of elevator systems and to avoid congestion, especially in tall buildings, the elevators may be implemented as multi-deck elevators. In multi-deck elevators, two or more elevator cars are arranged in the same frame structure, which moves in the elevator shaft as driven by the drive machine, so that the elevator serves several floors simultaneously when it stops. To ensure efficient operation of multi-deck elevators, the entrance lobby of the building is often divided into two or more waiting lobbies, which are interconnected e.g. by escalators. In this case, the destination call devices can be disposed either in the waiting lobbies in the immediate vicinity of the elevators, or in a centralized manner in the entrance lobby, from where passengers are guided via escalators into the waiting lobby according to the allocated route and further to the elevator serving the passenger.
As mentioned above, multi-deck elevators are able to serve even large numbers of passengers effectively, e.g. during up-peak conditions as people are arriving at their jobs in the mornings and the main direction of traffic is from the entrance lobby to upper floors in the building. However, it has been established that, in certain traffic situations, e.g. at lunch time, where the direction of traffic flow is from the entrance lobby to the upper floors of the building or vice versa and at the same time inter-floor traffic occurs within the building, the transport capacity of multi-deck elevators may be reduced significantly when both peak traffic and inter-floor traffic have to be served by multi-deck elevators. The problem may be aggravated in destination control systems, where an elevator is immediately allocated to serve a passenger having entered a call (and the passenger is given corresponding information). In this case, the group control has no chance to subsequently change the elevator serving the call and is therefore unable to optimize the selected elevator routes, whereas such possibilities are available in elevator systems using the traditional up/down call entry method. Allocation performed immediately on the basis of a call may thus be unfavorable when new calls are to be allocated after a previously entered call, leading to underutilization of the capacity of the elevator system.
The use of multi-deck elevators also involves certain additional drawbacks. The multi-deck elevator is ill adapted for certain special applications, such as e.g. for use as a fire-fighting elevator, because in this application it may be required that, to provide the service capacity prescribed by elevator regulations, extra floor space be provided at the upper or lower end of the elevator shaft. Besides, multi-deck elevators are more complex in respect of both mechanical construction and control system as compared to single-deck elevators. The structural complexity of multi-deck elevators may also be increased as a result of variation in the floor heights of the building, because in such cases the multi-deck elevator has to be provided with a mechanism that allows the mutual distance between the elevator decks to be varied according to the floor height so as to permit simultaneous service to the floors in question. On the whole, the use of multi-deck elevators increases the acquisition and maintenance costs of elevator systems, and therefore multi-deck elevator systems are expensive. A possible approach to solve some of the above-described problems is to implement the elevator system using both single-deck elevators and multi-deck elevators in the same elevator system. Japanese application publication JP11130349, among others, discloses an elevator group comprising both single-deck elevators and double-deck elevators. This solution is based on a zoning arrangement in which the single-deck elevators and double-deck elevators serve different zones in peak traffic situations.